1. Field of the Invention
The present invention relates to copper alloys.
2. Description of the Related Art
A variety of copper alloys have been devised as high-strength copper alloy used for various types of springs, bearings and the like. For example, PTL 1 discloses a copper alloy that is a Ni—Sn—Cu-based spinodal alloy to which Mn been added to prevent grain boundary precipitation that my occur in copper alloy cast materials. According to PTL 1, when Cr, Mo, Ti, Co, V, Nb, Zr, Fe, Si or the like is added to this copper alloy, Ni—Sn—Mn, Si or those additive elements form a hard intermetallic compound that crystallizes out in the matrix, thus contributing to the increase of wear resistance and seizure resistance. PTL 2 discloses a copper alloy whose strength is increased without reducing the electric conductivity by adding Cr or Zr to copper, and further in which oxides of Cr or Zr are prevented from being formed by controlling the oxygen content to 60 ppm or less. This patent literature describes a technique for adding carbon to a molten material or a molten metal for reducing the oxygen content. Also, PTL 2 discloses that the strength of this copper alloy is increased by adding Ni, Sn, Ti, Nb or the like to the copper alloy, and that grain coarsening is prevented by adding Ti or Nb.